The present invention generally relates to a device for releasing fluid pressure from the pressure chamber of rotational control devices, particularly to a device for releasing fluid pressure from the pressure chamber of overload apparatus, and specifically to a device for releasing fluid pressure from the pressure chamber of overload clutches.
In certain installations, clutches have been installed in line with torque limiting devices to prevent transfer of torque to the load beyond a certain overload level. In many of such installations, the prior separate clutch and torque limiting device may be replaced with an overload clutch, one type of which is shown in U.S. Pat. No. 4,770,281. It can then be appreciated that fluid pressure in the pressure chamber of the clutch continuously seeks to rotatably relate the input and the output, even when the output is at a constant overload level. It may be desirable in certain circumstances to require that the operator reset the overload device rather than have the device automatically attempt to return to a drive condition. For example, it maybe desirable for the operator to investigate the cause of the overload for correction prior to restarting. Further, excessive wear at the clutch interface may occur when the clutch continuously seeks to rotatably relate the input and the output especially when the output exceeds the overload level.
Resetting features may be incorporated into overload clutches such as the type shown and described in U.S. Pat. No. 4,770,281 by dumping the fluid pressure from the pressure chamber of the piston and cylinder when separation occurs at the interface signaling an overload condition. When the fluid pressure is dumped, the spring bias separates the interface until the pressure chamber is again pressurized. Prior attempts to incorporate this feature utilized specially manufactured, axially arranged valves mounted to the cylinder and which directly abutted with the piston. With this arrangement, it is necessary to completely disassemble the clutch and often dismantle the clutch installation to repair or maintain the axial valve. Thus, considerable downtime may be experienced to repair or maintain a minor cost item in the clutch.
Thus, a need has arisen for a device for dumping fluid pressure from the pressure chamber to obtain resetting features in pressure actuated overload apparatus which is actuable and accessible from the exterior of the overload apparatus and which utilizes off the shelf components to eliminate the capitol costs associated with specially manufactured components.